In a healthy human body, glands in the lining of the nose, throat and airways produce about 1 to 1.5 liters daily of a thick, wet substance called mucus. The purpose of mucus is to help trap and destroy harmful bacteria and viruses in the airways before they can enter the body. Mucus produced in the nose is transported toward the throat and into the digestive system. This process is called mucociliary clearance and generally goes unnoticed, similar to breathing or blinking. However, viruses, infections, and the inhalation of airborne irritants, particles and micro-organisms can trigger an overproduction of mucus and/or thicker-than-usual mucus. This increased/thickened mucus causes irritation, which is known as post nasal drip syndrome (PNDS) or upper airway cough syndrome (UACS).
Nasal mucus is produced by the nasal mucosa and mucosal tissues lining airways (trachea, bronchus, bronchioles). Mucosal tissues include specialized airway epithelial cells (goblet cells) and submucosal glands. Goblet cells are situated in the epithelium of the conducting airways, often with their apical surfaces protruding into the lumen, a location which allows them to aid in a rapid response to inhaled airway insults. Goblet cells may have a much greater potential for mucus secretion than do the submucosal glands. Thus, goblet cells may represent the principal front-line defender of the airway.
New information demonstrates that goblet cells can discharge vast quantities of mucus in fractions of a second, a property integral to airway defense against acute insult. Goblet cells can also increase in number in response to continued airway insult. The increase in goblet cells, and hence mucus production, may be a result of hyperplasia (involving cell division) and/or metaplasia (involving cell differentiation). Preventing metaplasia may be achieved by eliminating goblet cell metaplasia inducing components, such as Interleukin (IL)-13. This gene encodes an immunoregulatory cytokine produced primarily by activated Th2 cells. This cytokine is involved in several stages of B-cell maturation and differentiation.
While the overproduction of nasal mucus can be a result of anatomical causes like deviated nasal septum and turbinate hypertrophy, non-anatomical causes, such as allergies, have also been known to trigger PNDS. These patients may have overactive immune systems, leading to an overproduction of mucus. The most straightforward method of treating the allergy problem is to take a test to diagnose the causes of allergies and making lifestyle changes to stay away from these causes. Medications like antihistamines are often prescribed to block allergy mediators. However, antihistamines may thicken mucus secretions and can worsen bacterial rhinitis or sinusitis. A specific antihistamine may lose its effectiveness over time, requiring more or alternative antihistamines to reduce systemic reaction. In addition, antihistamines may come with side effects such as headache, dry mouth, and dry nose.
Nasal-spray corticosteroids (commonly called steroids) are considered the most effective drugs for controlling the symptoms of moderate-to-severe allergic rhinitis. However, side effects may include dryness, burning, stinging in the nasal passage, sneezing, headaches and nosebleed. There may also be long term complications caused by hormone suppression, such as lower resistance to infection, effects on growth in children, nervousness, acne, etc. Cromolyn and leukotriene antagonists may have lesser side effects, but are not as effective as nasal corticosteroids. The major hazard with nasal-delivery decongestants, particularly long-acting forms, is a cycle of dependency and rebound effects. For oral decongestants, side effects such as insomnia, irritability, nervousness, and heart palpitations may be observed.
Immunotherapy (commonly referred to as “allergy shots”) is a safe and effective treatment for patients with allergies. The major downside to immunotherapy is that it requires a prolonged course of weekly injections. This makes the treatment process laborious and patients often fail to comply with the regimens, limiting the end results of the therapy.
Therefore, a need exists for a long lasting, single-treatment or low frequency treatment for PNDS caused by allergies, anatomical causes or other causes. Ideally, such a treatment would alleviate PNDS symptoms, without producing severe and/or chronic side effects.